Role of visual information in ball catching

The present study is concerned with the perceptual information about the body and space underlying the act of catching a ball. In a series of four experiments, subjects were asked to catch a luminous ball under various visual conditions. In general, catching in a normally illuminated room was contrasted with catching the luminous ball in an otherwise completely dark room. In the third and fourth experiments, intermediate conditions of visual information were included. The results suggest that it is possible to catch a ball with one hand when only the ball is visible, but performance is better when the subject has the benefit of a rich visual environment and two hands. The second experiment indicated that subject performance does improve with practice in the dark, but time spent in the darkened room itself doesn't result in a significant decrement in performance. Results of the third study suggest that vision of one's hand does not aid in the performance of this task whereas the presence of a minimal visual frame appears to aid performance. The final study examined the relation between catching performance and body sway under similar visual conditions. Results of this experiment imply that persons who exhibit relatively little postural sway in full-room lighting performed better at this catching task.     

Structuring of early reaching movements: a longitudinal study

Reaches, performed by 5 infants, recorded at 19 weeks of age and every third week thereafter until 31 weeks of age, were studied quantitatively. Earlier findings about action units were confirmed. At all ages studied, movements were structured into phases of acceleration and deceleration. Reaching trajectories were found to be relatively straight within these units and to change direction between them. It was also found that at all ages, there was generally one dominating transport unit in each reach. The structuring of reaching movements changed in four important ways during the period studied. First, the sequential structuring became more systematic with age, with the dominating transport unit beginning the movement. Second, the duration of the transport unit became longer and covered a larger proportion of the approach. Third, the number of action units decreased with age, approaching the two-phase structure of adult reaching. Finally, reaching trajectories became straighter with age.     

Getting the closer object? An information‐based dissociation between vision for perception and vision for movement in early infancy

In human adults two functionally and neuro‐anatomically separate systems exist for the use of visual information in perception and the use of visual information to control movements (Milner & Goodale, 1995 , 2008 ). We investigated whether this separation is already functioning in the early stages of the development of reaching. To this end, 6‐ and 7‐month‐old infants were presented with two identical objects at identical distances in front of an illusory Ponzo‐like background that made them appear to be located at different distances. In two further conditions without the illusory background, the two objects were presented at physically different distances. Preferential reaching outcomes indicated that the allocentric distance information contained in the illusory background affected the perception of object distance. Yet, infants' reaching kinematics were only affected by the objects' physical distance and not by the perceptual distance manipulation. These findings were taken as evidence for the two‐visual systems, as proposed by Milner and Goodale ( 2008 ), being functional in early infancy. We discuss the wider implications of this early dissociation.     

Fitting objects into holes: on the development of spatial cognition skills

The authors examined 14- to 26-month-old infants' understanding of the spatial relationships between objects and apertures in an object manipulation task. The task was to insert objects with various cross-sections (circular, square, rectangular, ellipsoid, and triangular) into fitting apertures. A successful solution required the infant to mentally rotate the object to be fit into the aperture and use that information to plan the action. The object was presented standing up in half of the trials; in the other half, it was lying down. The results showed that infants solved the problem consistently from age 22 months and that a successful solution was associated with appropriate preadjustments before the hand arrived with the block to the aperture. No sex differences were found.     

Predictive tracking over occlusions by 4-month-old infants

Two experiments investigated how 16-20-week-old infants visually tracked an object that oscillated on a horizontal trajectory with a centrally placed occluder. To determine the principles underlying infants' tendency to shift gaze to the exiting side before the object arrives, occluder width, oscillation frequency, and motion amplitude were manipulated resulting in occlusion durations between 0.20 and 1.66 s. Through these manipulations, we were able to distinguish between several possible modes of behavior underlying 'predictive' actions at occluders. Four such modes were tested. First, if passage-of-time determines when saccades are made, the tendency to shift gaze over the occluder is expected to be a function of time since disappearance. Second, if visual salience of the exiting occluder edge determines when saccades are made, occluder width would determine the pre-reappearance gaze shifts but not oscillation frequency, amplitude, or velocity. Third, if memory of the duration of the previous occlusion determines when the subjects shift gaze over the occluder, it is expected that the gaze will shift after the same latency at the next occlusion irrespective of whether occlusion duration is changed or not. Finally, if infants base their pre-reappearance gaze shifts on their ability to represent object motion (cognitive mode), it is expected that the latency of the gaze shifts over the occluder is scaled to occlusion duration. Eye and head movements as well as object motion were measured at 240 Hz. In 49% of the passages, the infants shifted gaze to the opposite side of the occluder before the object arrived there. The tendency to make such gaze shifts could not be explained by the passage of time since disappearance. Neither could it be fully explained in terms of visual information present during occlusion, i.e. occluder width. On the contrary, it was found that the latency of the pre-reappearance gaze shifts was determined by the time of object reappearance and that it was a function of all three factors manipulated. The results suggest that object velocity is represented during occlusion and that infants track the object behind the occluder in their 'mind's eye'.     

Action in development

It is argued that cognitive development has to be understood in the functional perspective provided by actions. Actions reflect all aspects of cognitive development including the motives of the child, the problems to be solved, and the constraints and possibilities of the child's body and sensorimotor system. Actions are directed into the future and their control is based on knowledge of what is going to happen next. Such knowledge is available because events are governed by rules and regularities. The planning of actions also requires knowledge of the affordances of objects and events. An important aspect of cognitive development is about how the child acquires such knowledge.     

Do infants reach for perceived objects? A reply to Stiles-Davis

Stiles-Davis proposes that the infants in our experiments (Hofsten & Spelke, 1985) did not reach for perceived objects in order to manipulate them, but rather touched perceived surfaces in order to explore their boundaries. Her commentary raises questions about infants' perception of the boundaries, the unity, and the manipulability of objects. More deeply, it raises the question of what an object is for an infant. We consider each of these questions in turn, in light of our own findings and those of other studies of object-directed reaching, object perception, and the object concept. We suggest that young infants organize the visual world into entities that are bounded, unitary, and manipulable and that infants endow those entities with the core properties of physical objects.     

The role of binocular information in ball catching

The role of binocular vision in a ball-catching task involving spatial uncertainty was examined in three experiments. In all three experiments, subjects' catching performance was evaluated during monocular and binocular viewing, in normal room lighting and in complete darkness with a luminescent ball. Subjects' performance was found to be significantly better with binocular than with monocular vision, especially under normal lighting conditions. In the second and third experiments, catching performance was evaluated in the presence of minimal visual frames, consisting of a series of light-emitting diodes (LEDs). In Experiment 2, the visual frame consisted of a single plane of LEDs, whereas in Experiment 3, the visual frame consisted of two planes of LEDs. Catching performance was found to be significantly better with the visual frame than in complete darkness, but this was true only for binocular viewing. This result supports the hypothesis that binocular convergence is used to scale perceived space and that this information enables subjects to contact the ball successfully. It was further found that postural sway varied between lighting conditions and that less sway was accompanied by higher performance. There was no effect of binocular viewing in this respect. In general, the results suggest two additive effects of viewing conditions: a direct effect of binocular vision on ball catching and an indirect effect of lighting on postural stability, which, in turn, affects catching performance.     

Proximal velocity change as a determinant of space perception

How and to what degree does proximal velocity change determine perceived translatory motion in depth? This question was studied with a stimulus consisting of a single dot, moving in a straight horizontal path in a frontoparallel plane. Its motion corresponded to distai depth motion with constant speed. Ss reported verbally what they perceived. The results show that proximal velocity changes of this kind are, within certain limits, utilized by the visual system for the perception of translatory motion in depth. The limits were found to be determined by the absolute rate of change in proximal velocity. Further, it was found that the perceived motion track was usually bent, although all stimuli simulated depth motions along straight paths.